The electric power industry has for many years recognized that thermal decomposition of the oil and other insulating materials within oil-insulated electrical apparatus can lead to the generation of a number of “fault gases.” These phenomena occur in equipment such as oil filled transformers (both conservator and gas-blanketed types), load tap changers, transformer windings, bushings and the like. The detection of specific fault gases in electrical apparatus can be an important part of a preventative maintenance program.
The presence of fault gases in oil-blanketed transformers with conservators and other utility assets has well documented implications relating to the performance and operating safety of the transformer. There is a substantial body of knowledge available correlating the presence of gases with certain, identified transformer conditions and faults. It is therefore beneficial to monitor the condition of dielectric fluids in electric equipment as a means to maximize performance, and at the same time minimize wear and tear on the equipment, and to thereby minimize maintenance costs and down time. Thus, information relating to the presence or absence of certain fault gases in transformer oil can lead to greatly increased efficiency in the operation of the transformer.
The presence of certain fault gases in transformer oil can be indicative of transformer malfunctions, such as arcing, partial or coronal discharge. These conditions can cause mineral transformer oils to decompose generating relatively large quantities of hydrogen gas, which is highly volatile, and which in some instances may accumulate in a transformer under relatively high pressure. Left undetected or uncorrected, equipment faults can lead to an increased rate of degradation, and even to catastrophic explosion of the transformer. Transformer failure is a significantly expensive event for an electric utility, not only in terms of down time and the costs of replacement equipment, but also in terms of the costs associated with lost power transmission. From a safety perspective, it is imperative that line personnel and maintenance crews know if a particular operating transformer contains dangerous levels of hydrogen gas before approaching the unit. A visual indicator that indicates when hydrogen gas is present and which can be viewed from a safe distance, aided if necessary with a spotting scope, would provide a warning so that the transformer can be de-energized and removed for maintenance.
Despite the known need for reliable equipment to monitor gas in oil, designing equipment that holds up to the rigors of on-site conditions has been problematic for a variety of reasons. That said, there are a number of solutions known in the art. For example, mechanical/vacuum and membrane extraction methods and apparatus for degassing transformer oil are well known, as exemplified by U.S. Pat. No. 5,659,126. This patent discloses a method of sampling headspace gas in an electrical transformer, analyzing such gases according to a temperature and pressure dependent gas partition function, and based on the derived analysis predicting specific transformer faults.
An example of a gas extraction apparatus that relies upon a membrane tube for extraction of gas from transformer oil is disclosed in U.S. Pat. No. 4,112,737. This patent depicts a plurality of hollow membrane fibers, which are inserted directly into transformer oil in the transformer housing. The material used for the membrane is impermeable to oil, but gases dissolved in the oil permeate through the membrane into the hollow interior of the fibers. A portable analytical device such as a gas chromatograph is temporarily connected to the probe so that the test sample is swept from the extraction probe into the analytical device for analysis.
Although these devices have provided benefits, they have significant limitations when used to monitor smaller transformers used in connection with, for example, pole-mounted distribution transformers used by electric utilities. Not only are these types of transformers too difficult to access for routine monitoring, but the costs and difficulties associated with either extracting gas from or installing extractors into such small devices makes the foregoing types of monitoring unpractical.
Moreover, there are numerous practical problems remaining to the development of reliable apparatus for extraction, monitoring and analysis of fault gases in transformer oils. Many of these problems relate to the design of reliable fluid routing systems that are redundant enough to provide a relatively maintenance free unit. Since transformers are often located in exceedingly harsh environmental conditions, fluid routing problems are magnified. This is especially true given that the instruments needed to reliably analyze the gases are complex analytical instruments. Two patents that describe the difficulties of these engineering challenges are U.S. Pat. Nos. 6,391,096 and 6,365,105, both of which are incorporated herein by this reference. These two patents illustrate not only the complexities of the fluid routing systems needed, but solutions that have proved very reliable.
In addition to the examples given above, there are numerous other devices available for monitoring electrical asset oil for the presence of hydrogen and other gases. However, such devices tend to be very expensive and are therefore limited to larger electrical assets—the costs of the equipment and the monitoring programs that go with them are too high to justify using the devices with relatively smaller assets such as transformers used by utilities for routine power delivery systems. But the problems with fault gas accumulation in transformers are not limited to the large systems that can be monitored with existing systems such as those described above and the expenses that are caused by transformer failure are a significant part of many utilities' business. Accordingly, there is a need for a low cost device that allows utilities to monitor transformers to detect the presence of hydrogen.